STABILITY OF LiNiCoAl-OXIDE ELECTRODE MATERIAL UNDER HIGH-TEMPERATURE CERAMIC FUEL CELL CONDITIONS

Abstract

LiNi0.8Co0.15Al0.05O2 (LNCA) is an important cathode material for room-temperature operation of lithium-ion batteries (LIBs). As an emerging research area, LNCA was recently applied as electrodes (both cathode and anode) for high-temperature ceramic fuel cells (CFCs) with impressive performances. However, the stability of LNCA electrode material under CFC operating conditions (i.e., reactive atmospheres and high temperatures) remains unknown. In this dissertation: (1) The stability of LNCA in air and H2 atmospheres was systematically evaluated at elevated temperatures (i.e., the operating electrode environments of H2-fueled CFCs). It was found that LNCA exhibited excellent stability in air within a wide temperature range from 25 to 800 °C. However, the H2 atmosphere caused the decomposition of LNCA into LiOH and NiO/CoO solid solution at 300 °C, followed by complete reduction of NiO/CoO to Ni/Co alloy at 600 °C. The H2-promoted decomposition was identified as a near second order reaction with an activation energy of 223.59 kJ mol-1. These findings indicate that LNCA can be used as a stable cathode material and it is a suitable precursor for the in-situ formation of Ni/Co-based anode materials for H2-fueled CFCs. (2) The stability of LNCA in CH4 and CO2 was investigated at elevated temperatures (i.e., the anode conditions of CH4-fueled CFCs). It was found that LNCA started to react with CH4 at 500 °C, leading to its decomposition into Li2CO3, NiO/CoO solid solution, Ni/Co alloy, and LiAlO2. The NiO/CoO solid solution was further reduced into Ni/Co by CH4 at 600 °C. Furthermore, CO2 could make LNCA decomposed into Li2CO3, NiO/CoO, and Al2O3 starting at 600 °C. These results can be used to design efficient electrodes for CH4-fueled CFCs using LNCA as a precursor. (3) Stability of LNCA was also examined in CO-fueled conditions. The CO-induced decomposition of LNCA generated Ni/Co alloy, Li2CO3, LiAlO2 and carbon at temperatures of 500 °C or above. Overall, the decomposition of LNCA under CFC operating conditions must be considered when using LNCA as electrodes in practical CFC devices.